Device for transmitting pictures telegraphically



Dec. 29, 1931. w. SCHEPPMANN DEVICE FOR TRANSMITTING PICTURESTELEGRAPHICALLY Filed Feb. 7, 1929 Patented Dec. 29, 1931 UNITED STATESPATENT OFFICE WILHELM SGHEPPMANN; OF BERLIN-NEUTEMPELHOF, GERMANY,ASSIGNOR To C. LORENZ AKTIENGESELLSCHAFT, OF BERLIN-TEMPELHOF, GERMANYDEVICE FOR TRANSMITTING PICTURES TELEGRAPHICALLY Application filedFebruary 7, 1929, Serial No. 338,068, and in Germany February 15, 1928.

In systemsadaptedfor the transmission of pictures it is customary toplace the lightsensitive cell in the grid circuit of the input tube ofan amplifying device and to modulate an alternate current introduced inthe way of the said boosting device. Only in this way it is possible toeasily further amplify the rather wide band of frequencies of thevariations of current produced by the scanning of the picture. In orderto avoid the introduction of an alternate frequency it was suggested toapply to the light-sensitive cell a ray of light of varying intensity.For that purpose a rotating perforated disc is usually placed in thepath of the light between a source of light and the light-sensitivecell, in order to interrupt the ray of light perlodically. In thismanner a current of varying energy is obtained in the photoelectriccell, which current can be intensified in known manner by means of anysuitable amplifying device. In carrying out this method difficultieswill be caused due to the use of the said perforated disc. In order toobtain a sufficiently high number of interruptions of the ray of lightper second, it is necessary to employ perforated discs of large size.Through this vibrations of the picture transmitting apparatus areunavoidable.

According to the present inventionrthese drawbacks are obviated in thatthe ray of light is acting periodically upon the light sensitive cellthrough a control device as for instance, a string galvanometer, anoscillograph or the like.

A mode of execution of'the picture transmitting device according. to theinvention is shown by way of example diagrammtically on the drawing.

The picture drum B is driven by a motor M by the intermediary of a gearwheel Z mounted on the shaft of said picture drum. A high frequencydynamo is coupled with the driving motor and designated HF. The

device 0 is concentrated upon the light conhigh frequency currents(ranging. between trol device G. On the drawing a known stringgalvanometer is shown as such is customary in the transmission ofpictures. The ray of light after passing through the slot of thegalvanometer is concentrated by means of the optical lens 0 upon thepicture drum and the reflected light is passed through the opticaldevice lens 0 to the light sensitive cell S, included in the gridcircuit of the input tube R of an amplifier. A suitable biasing Voltageis applied to the light-sensitive cell by the battery B while thebatteries B and B respectively represent the heating and anode batteriesfor the tube R.

Through the transformer U connected to the anode circuit of the tube thecurrents are passed to an additional amplifier not illustrated. As thegalvanometer string will oscillate with the frequency of the currentgenerated inthe high frequency machine, a periodically interruptedcurrent, which can be efliciently amplified, is flowing through theanode circuit of the tube R.

A further advantage of the arrangement consists in that with afluctuating number of revolutions of the driving motor of the picturetransmission device, the number of cycles of the high frequencygenerator will fluctuate in the same proportion and in consequence thenumber of openings of the light control apparatus will remain the samefor each point of the picture.

I claim:

In a picture transmitter, a picture to be transmitted, a source oflight, a motor, means controlled by said motor for impinging light fromsaid source on successive points of said picture to scan said picture, agalvanometer, a string light valve placed in the path of the light fromsaidgsource to said picture, a source of alternating currents controlledby said motor and electrically connected to said jgalvanometer foroscillating said galvanometer at a predetermined frequency, having adefinite relation with said speed of scanning, whereby said lightis-cor'respondingly varied at the predetermined frequency.

In testimony whereof I have aflixed my signature.

WILHELM SCHEPPMANN;

